JP3872698B2 - Steel plate with excellent laser cutting ability and its manufacturing method - Google Patents

Description

【００２０】
【表２】

【００２１】
尚、表２に示すスケール厚は、鋼板を圧延後、常温まで冷却した後、サンプルを採取し、光学顕微鏡または走査型顕微鏡を用いて測定した値である。
また、スケールの組成は、前記サンプルをＸ線回析して測定した値である。
更に、スケール密着性は、鋼板に５％の引張歪みを与えて、40mmx50mmの面積当たりに剥離したスケール量であり、そのスケール量は、電子天秤で測定した値である。
また、切断結果は、鋼板を出力６ｋＷのレーザーで７５０〜１２００ｍｍ／ｍｉｎの切断速度で１ｍ切断した際において、その切断面を目視観察したものであり、◎は切断面のノッチが１個以下である。△は切断面に２個以上のノッチがある。×は切断中にバーニングが発生し、切断不可能となった。
【００２２】
表２からわかるように、本発明例１〜４は良好なレーザーでの切断結果を得た。
これに対して、比較例１は、デスケーリングを行わなかったパスがあり、比較例２は、デスケーリング圧力が１００ｋｇ／ｍｍ ² 以下であることから、何れもレーザーでの切断結果が悪いものであった。
【００２３】
【発明の効果】
以上説明したように、本発明によれば、鋼板のスケール密着性が向上し、レーザー切断に際しての熱衝撃によるスケールの剥離を防止できるため、安定して良好な切断面が得られ、産業上有用な著しい効果を奏する。
【図面の簡単な説明】
【図１】マグネタイト比率とスケール剥離率の関係を示す図である。
【図２】デスケーリング方法を示す図である。
【図３】デスケーリング圧力とマグネタイト比率の関係を示す図である。
【図４】５％引張剥離試験片を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel sheet having a good laser cut surface and a method for producing the same.
[0002]
[Prior art]
A large amount of heavy steel plates are used in steel structures such as shipbuilding, construction, industrial machinery, and bridges, but in the work of these steel structures, most of the construction costs and man-hours are occupied by welding and cutting. Yes. Conventionally, as a method for cutting the thick steel plate, there are gas cutting, plasma cutting, laser cutting and the like.
[0003]
This laser cutting is a cutting method that has been put into practical use since about 20 years ago, and has been popularized mainly in the thin plate processing industry with a plate thickness of 3.2 mm or less. The use is expanding to cut thick steel plates.
[0004]
This laser cutting is a method in which a material and an oxide are melted by the thermal energy of laser light, and the melt is removed with an assist gas to form a cut groove. The maximum plate thickness that can be cut is about 25 mm, but the cutting groove width is narrow and suitable for precision cutting, and the cutting distortion is the smallest in thermal cutting. In addition, there are various types of materials that can be cut in thermal cutting, and cutting of complicated shapes is possible. Furthermore, since the cutting work can be automated, the introduction of facilities is rapidly progressing as a rationalization measure for companies.
[0005]
However, in the thick steel plate, since the range of the appropriate laser cutting speed is limited, expansion of the application range has been hindered. That is, if the cutting speed is increased, the energy efficiency per unit cutting length is reduced, and the entire plate thickness cannot be melted or even if it can be melted, the molten metal cannot be sufficiently removed. There arises a problem that the molten metal adheres to the lower surface of the cut as dross.
[0006]
On the other hand, when the cutting speed is reduced, the cutting width is increased and the amount of molten metal is increased, so that the cutting width is increased, and uneven cut portions having irregularities called notches are generated on the cut surface. The notch on the cut surface has an adverse effect on the welding and processing of the steel sheet, and therefore requires a great load with the work of finishing the cross section with care. Accordingly, there is a demand for a thick steel plate having stable laser cutting properties.
[0007]
For the purpose of improving the laser cutting property, many attempts have been made to improve the properties of the scale of the steel sheet. For example, as proposed in JP-A-11-61248, the scale thickness is reduced to 6 μm or less. , There is a method for producing a steel sheet containing 60 vol% or less of magnetite.
[0008]
[Problems to be solved by the invention]
However, if the amount of magnetite in the scale is 60 vol% or less, the adhesion of the scale is inferior, and if the plate thickness is 19 to 25 mm, the effect of improving the laser cutting property is not sufficient. That is, the notch may occur.
As described above, it is an object of the present invention to provide a steel plate having excellent laser cutting ability and a method for manufacturing the same, in which notches are not generated on the cut surface.
[0009]
[Means for Solving the Problems]
The present invention has been made to solve the above problems,
The means 1 is mass%,
C: 0.19 to 0.22%,
Si: 0.05 to 0.50%,
Mn: 0.6% or less,
P: 0.025% or less,
S: 0.015% or less,
Al: 0.045% or less,
N: steel plate containing 0.009% or less, the balance being iron and unavoidable impurities, the thickness of the scale formed on the surface is 6 μm or less, and the scale is made of magnetite having a volume of 85 vol% or more It is a steel plate with excellent laser cutting properties.
Means 2 further comprises mass%,
Ni: 0.5% or less,
Cu: 0.5% or less,
Mo: 0.4% or less,
Cr: 0.5% or less,
Nb: 0.04% or less,
V: 0.08% or less,
It is a steel plate excellent in laser cutting property containing one kind or two kinds or more.
Furthermore, the means 3 starts the rolling after heating the steel plate having the component described in the means 1 or 2 to 950 ° C. to 1250 ° C. in a heating furnace, and 100 kg / mm ² or more in all passes during the rolling. The thickness of the scale formed on the surface of the steel sheet is set to 6 μm or less by performing rolling at 850 ° C. to 950 ° C. while descaling at a water pressure of 5 vol. It is a manufacturing method of the steel plate excellent in the laser cutting property characterized by making.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As a result of examining the notch generation mechanism that occurs on the cut surface when the steel sheet is cut with a laser, the inventors have found that when the steel sheet is moved by moving the laser, the width at which the steel sheet melts is different. As a result, it was found that the notch was caused by peeling of the scale on the surface of the steel sheet due to the thermal shock of the laser.
In order to prevent the peeling of the scale, it is important to improve the adhesion of the scale, which can prevent the peeling of the scale at the time of laser cutting if the adhesion of the scale is improved. The same width is obtained, and stable cutting quality can be obtained. In addition, a wide range of cutting speeds for obtaining good cutting quality can be taken, and workability is improved.
To prevent scale peeling from the steel plate surface during laser cutting,
The scale thickness must be 6 μm or less, and the amount of magnetite in the scale must be 85 vol% or more. For this purpose, the front and back surfaces of the steel sheet are descaled with a hydraulic pressure of 100 kg / mm ² or more in all rolling passes during rolling. However, it has been found necessary to finish the rolling at 850 ° C. to 950 ° C.
[0011]
The reason will be described below.
First, as a result of investigating the relationship between the ratio of magnetite (Fe 3 O 4) in the scale formed on the steel sheet surface and the peeling rate of the scale, it was found that there is a relationship shown in FIG.
The scale used in FIG. 1 is composed of wustite, hematite, and magnetite, has a thickness of 6 μm, and the peel rate of the scale is 5% strain applied to the flat tensile test piece. The amount of scale peeled off from the area of the parallel part (40 mm × 50 mm) of the tensile test piece shown was measured and calculated.
As can be seen from FIG. 1, when the amount of magnetite is 85 vol% or more, it has been found that the peeling rate of the scale rapidly decreases. This is presumably because the scale is dense and has high strength, the adhesion between the steel plate of the steel sheet and the scale is improved, and the scale is prevented from being peeled and scattered by thermal shock during laser cutting.
[0012]
Furthermore, the scale thickness needs to be 6 μm or less. As the scale thickness becomes thicker than 6 μm, the thermal shock received by the scale during laser cutting increases, cracks occur in the scale, and the scale surface partially peels off. However, since the notch is generated due to a difference in the scale thickness, the thickness is set to 6 μm or less which does not cause partial peeling of the scale surface.
[0013]
Next, manufacturing conditions for generating a scale having a thickness of 6 μm or less and containing 85 vol% or more of magnetite will be described.
The scale on the surface of the steel sheet occurs when the steel sheet is in a high temperature state of 850 ° C. to 950 ° C. or higher, and hardly occurs thereafter. And first, it produces | generates as a scale which consists of wustite (FeO), and this wustite transforms into a magnetite as a steel plate cools after that. For this reason, in order to make the thickness of a scale thin, it is necessary to suppress that a scale generate | occur | produces on the steel plate front and back in the high temperature state of 850 degreeC-950 degreeC or more.
[0014]
In order to suppress this generation of scale, descaling for injecting cooling water to the entire front and back surfaces of the steel sheet on the entry side and exit side of the rolling roll as shown in FIG. 2 is necessary. Furthermore, the steel plate front and back surfaces are cooled by this descaling, and wustite generated on the steel plate front and back surfaces is transformed into magnetite.
In this descaling, as shown in FIG. 3, in order to obtain a magnetite ratio in the scale of 85 vol% or more, the descaling water pressure is 100 kg / mm ² or more, and from the first pass of rolling to the final finishing pass. Must be done in all passes.
In FIG. 3, a slab heated at a plate thickness of 200 mm and 1200 ° C. was rolled in 10 passes, and the rolling was completed at a plate thickness of 22 mm and a finishing temperature of 900 ° C.
The reason why the descaling water pressure needs to be 100 kg / mm ² or more is assumed to be because water remaining on the surface of the steel sheet can be prevented, and the front and back surfaces of the steel sheet can be cooled uniformly. The
Further, by performing descaling in all passes, it is possible to prevent the temperature of the front and back surfaces of the steel sheet from rising due to recuperation, so that the scale can be reliably made magnetite.
[0015]
Below, the restriction | limiting range of each element contained in a steel plate is demonstrated.
C is a strong element and needs to be 0.03% or more, but if it exceeds 0.22%, the toughness of the steel sheet is deteriorated, so 0.22% was made the upper limit. Si deteriorates the laser cutting property, but has the function of improving the scale adhesion, so that the range of 0.05 to 0.50% is obtained by balancing the two.
Mn is an element that improves the scale adhesion without significantly degrading the laser cutting property. However, if it exceeds 1.6%, the weldability deteriorates, so 1.6% was made the upper limit.
[0016]
P and S have little influence on laser cutting property, but the lower the material, the better. P is set to 0.025% or less and S is set to 0.015% or less.
Al is necessary for deoxidation and is set to 0.045%.
If N is 0.0090% or less, it does not adversely affect weldability and slab quality. Although it is possible to produce a steel plate excellent in laser cutting property within the range of the steel plate components described above, it is effective to add the following elements in order to obtain higher strength without impairing the properties. .
[0017]
Ni, Cu, Mo, and Cr are solid solution strengthening elements and can increase the strength of the steel sheet. However, addition of a large amount impairs weldability economically and in quality, so the upper limit values are Ni ≦ 0.5%, Cu ≦ 0.5%, Mo ≦ 0.4%, Cr ≦ 5, respectively. %.
Nb and V are precipitation strengthening elements and have the effect of increasing the strength of the steel sheet. However, since a large amount of addition deteriorates the toughness of the welded portion economically and in quality, the upper limit values are set to Nb ≦ 0.04% and V ≦ 0.08%, respectively.
[0018]
【Example】
Tables 1 and 2 show examples of the present invention, and Table 2 shows a steel slab formed by continuous casting after melting steel having the composition shown in Table 1 and rolled immediately or after reheating. is there.
[0019]
[Table 1]

[0020]
[Table 2]

[0021]
The scale thickness shown in Table 2 is a value measured using an optical microscope or a scanning microscope after a steel sheet is rolled and then cooled to room temperature, and then a sample is taken.
The composition of the scale is a value measured by X-ray diffraction of the sample.
Furthermore, the scale adhesion is a scale amount that peels per 40 mm × 50 mm area by giving a tensile strain of 5% to the steel sheet, and the scale amount is a value measured by an electronic balance.
The cutting results were obtained by visually observing the cut surface when the steel plate was cut 1 m with a laser of 6 kW output at a cutting speed of 750 to 1200 mm / min. is there. Δ has two or more notches on the cut surface. X: Burning occurred during cutting, and cutting was impossible.
[0022]
As can be seen from Table 2, Examples 1 to 4 of the present invention obtained cutting results with a good laser.
In contrast, Comparative Example 1 has a path where descaling was not performed, and Comparative Example 2 has a descaling pressure of 100 kg / mm ² or less. Met.
[0023]
【The invention's effect】
As described above, according to the present invention, scale adhesion of the steel sheet is improved, and scale peeling due to thermal shock at the time of laser cutting can be prevented, so that a stable and excellent cut surface can be obtained, which is industrially useful. There is a remarkable effect.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a magnetite ratio and a scale peeling rate.
FIG. 2 is a diagram illustrating a descaling method.
FIG. 3 is a diagram showing a relationship between a descaling pressure and a magnetite ratio.
FIG. 4 is a view showing a 5% tensile peel test piece.

Claims (3)

% By mass
C: 0.19 to 0.22%,
Si: 0.05 to 0.50%,
Mn: 0.6% or less,
P: 0.025% or less,
S: 0.015% or less,
Al: 0.045% or less,
N: 0.009% or less, the balance being steel and iron and inevitable impurities,
A steel plate excellent in laser cutting property, wherein the scale formed on the surface has a thickness of 6 μm or less and the scale is made of magnetite having a volume of 85 vol% or more. Furthermore, in mass%,
Ni: 0.5% or less,
Cu: 0.5% or less,
Mo: 0.4% or less,
Cr: 0.5% or less,
Nb: 0.04% or less V; 0.08% or less,
1 or 2 types or more of these are contained, The steel plate excellent in the laser cutting property of Claim 1 characterized by the above-mentioned. The steel sheet having the component according to claim 1 or 2 is heated to 950 to 1250 ° C. in a heating furnace, and then rolling is started and descaling is performed at a water pressure of 100 kg / mm ² or more in all passes during the rolling. However, the rolling is finished at 850 ° C. to 950 ° C., and then air-cooled, whereby the thickness of the scale formed on the surface of the steel sheet is 6 μm or less, and the scale is made of magnetite having a volume of 85 vol% or more. The manufacturing method of the steel plate excellent in laser cutting property.

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